1. Field of the Invention
The present invention relates to the field of hearing aids. The invention, more specifically, relates to a method for the fitting of a hearing aid, to a system for fitting a hearing aid and to a hearing aid.
2. Description of the Related Art
U.S. Pat. No. 4,548,082 provides a hearing aid and a host computer for supplying sets of signals to the hearing aid in a total system. The host computer controls the emission of stored sounds by a loudspeaker. The host computer displays hearing threshold, most comfortable loudness level, uncomfortable loudness level, and performance characteristics of the hearing aid (e.g. mapping conversational speech onto the auditory area). The operator may enter adjusted values of gains, and the host computer computes how the hearing aid would, if programmed with the adjusted values, reposition the conversational speech spectrum on the stationary auditory area. The informational display shows the auditory area with the repositioned conversational speech spectrum (hearing aid response curves). Adjusted and unadjusted values of various of limits and gains are also output for operator reference.
DE-B4-10064210 provides a system for the testing of a hearing aid, wherein a fitting computer can read out and display input levels and output levels of sound in respective frequency bands.
It is nowadays a standard practice to fit hearing aids in an interactive session, the hearing aid user wearing a hearing aid, while a fitter remotely programs it and plays back sound to the user in order to provide him or her with an immediate acoustic impression of the performance of the hearing aid. The user comments to the fitter about his or her perceptions and about any perceived problems, and the fitter may then suggest adaptations and fine tunings of the settings and may program them into the hearing aid and again play back sound samples for letting the user try the adapted settings.
Traditionally hearing aids have been fitted to the hearing loss of the user using playbacks of standardized recordings of sound. These recordings reflect typical sound environments, such as street noise, party noise, dialogue, etc. Using these recordings the user can try out different settings and comment to the fitter, who can then adapt the parameters according to which the hearing aid modifies input sounds, so as to provide the best possible compensation for the hearing loss of the user, in various situations.
Advanced hearing aids may include several programs or schemes among which the user can choose depending on the current sound environment or listening situation, each of these programs being defined by a set of parameters, which can be programmed and tuned by the fitter. Parameters programmable for respective schemes are amplification in specific frequency bands, weighting of signals from different input transducers in order to provide various degrees of directionality, feedback suppression, adaptive noise reduction etc.
As the long-term statistical distributions of the pre-recorded samples of loud and soft signals are known, static curves illustrating the distributions are typically preprogrammed for ready presentation to the fitter during the fitting session. This presentation may simply be of the statistical distribution of the input signal itself, or the presentation may be of the statistical distribution of the output signal, which would be produced by the hearing aid based on the input signal and the current settings of the hearing aid. The presentation of the statistical distribution allows the fitter to assess and consider signals for judging what the hearing aid should do and for guidance in the event further adaptation might be requested.
There is however a desire from the users of hearing aids to have the fitting performed on actual sound recordings from the environments in which they find themselves, e.g. actual recordings from their workplace or other places of interest to the user. Such recordings are commonly referred to as “life sounds”. By fitting the hearing aid to the user using sounds from the actual environment, the performance of the hearing aid may be better adapted to those particular environments that are important to the user, as compared to a fitting using standardized sounds.
However, the use of life sounds, which are not standardized, presents the fitter with new problems when fitting the hearing aid.
One such problem is that the statistical distribution of the “life sounds” is unlikely to match any of the pre-programmed statistical distributions, so that these cannot be used. Moreover, as there is an infinite number of life sounds with different distributions, it is almost impossible for the fitter to gain any experience as to how the distribution is in any specific type of signal, and how it would be represented on the display during fitting.
Another problem stems from the fact that modem hearing aids include automated functions, i.e. functions that are activated by the hearing aid itself, such as adaptive directionality, adaptive feedback suppression, adaptive noise reduction, speech enhancement, variable signal gain or compression, etc. With sounds other than the standardized sounds it is not obvious to the fitter how the automated adaptive functions influence the final output, i.e. to the fitter there is a loss of transparency in what the hearing aid does to the input signals.
A further problem in relation to the transparency of the automated adaptive functions, in particular in the noise reduction or speech enhancement systems, is that a transient or short-term change of the spectral distribution may cause changes in the way those systems operate. In particular a change in the spectral distribution may alter the masking relations between the sounds, i.e. the fact that a sound with a given frequency and a high sound level, makes inaudible sounds at frequencies close to that frequency but having lower sound levels.